Recent requirements from the automotive industry for reduced engine power consumption have dictated the replacement of the power steering hydraulic pump with a more efficient electric motor geared to the steering shaft to assist the steering effort. The main difficulty has been with sensing the effort being applied by the driver so as to know how much to assist in the steering effort.
One sensor for sensing such effort applied by the driver is disclosed in U.S. Pat. No. 6,564,654 entitled “Vertical Movement Capacitive Torque Sensor.” This patent discloses using capacitive sensing technology, in which capacitances formed using two concentric ring plates are varied depending on the location of a dielectric material. The sensor has a plurality of dielectric vanes that move perpendicularly to an axis of rotation of the shaft on which the sensor is mounted. In one exemplary embodiment of this patent, each vane is biased by a biasing member to realize such movement in the perpendicular direction. Any such biasing member may introduce undesirable and/or unpredictable forces or torques into the sensor.
Therefore, it is desirable to provide an apparatus and method for sensing the driver's effort without biasing the dielectric material.